Add halo-theme-dev skill & theme templates

Add a new .agents/skills/halo-theme-dev skill providing Halo theme development resources: two theme templates (theme-vite and theme-minimal) with theme.yaml/settings, Vite config, package.json, CSS and JS assets, and a full set of Thymeleaf template files/partials. Include comprehensive reference docs (structure & config, finder APIs, global variables, annotations, static resources, packaging, official plugins, thymeleaf tips) and an agents/openai.yaml interface. Also update project files: modify package.json, update tsconfig.json, add skills-lock.json, rename vite-env.d.ts and remove obsolete src/main.ts and src/styles/main.css while populating src/ with the new template files.

src/page.html

@@ -0,0 +1,20 @@
+<include src="layout.html">
+  <template name="head">
+    <title th:text="|${singlePage.spec.title} - ${site.title}|">Page Title</title>
+  </template>
+
+  <article>
+    <header class="article-header">
+      <h1 class="article-title" th:text="${singlePage.spec.title}"></h1>
+    </header>
+    <div class="article-content" th:utext="${singlePage.content.content}"></div>
+  </article>
+
+  <div th:if="${haloCommentEnabled}">
+    <halo:comment
+      group="content.halo.run"
+      kind="SinglePage"
+      th:attr="name=${singlePage.metadata.name}"
+    />
+  </div>
+</include>